The present invention relates to a tire model determining method for determining a first-order lag model which simulates a transient response of a tire from measurement data of a lateral force or a longitudinal force, or from other measured transient response data of the tire which is obtained by giving a rolling tire a temporally varying physical amount that sets a tire rolling condition, for example, the applied load or the slip ratio in the longitudinal direction of the tire, a tire transient response data calculating method for calculating transient response data of a tire, which is generated by giving the rolling tire desired time-series data of the physical amount that sets a tire rolling condition, and a tire evaluating method and a tire designing method using the former two methods.
A tire is the only member which is interposed between a vehicle and the road surface and transfers a force from the road surface to the vehicle, so tires play an important role in today's automobile industry which seeks advanced vehicle control for safe vehicle driving and avoidance of danger. Analyzing a cornering characteristic of a tire is therefore necessary.
There is known a method disclosed in JP 2005-88832 A, in which a cornering characteristic of a tire in a steady state when a slip angle is given as time-series data is calculated based on a tire dynamic model that is built from multiple tire dynamic element parameters. The publication claims that in this way, a tire can be designed efficiently.
The above tire dynamic model can provide a cornering characteristic in a steady state by supplying a slip angle, but is not capable of simulating a transient response of the longitudinal force which changes with time by supplying a temporally varying value of the slip ratio in the longitudinal direction.
Further, today's vehicles are braked usually with the use of an anti-lock brake system (ABS), which controls the slip ratio on a few Hz basis so that the maximum braking force is always obtained upon braking. The generated braking force is therefore based on a characteristic obtained in a transient state which differs from that in a steady state. This characteristic differs from a characteristic when the braking force is operated in a steady state. Accordingly, there is an inability to evaluate the characteristic of a vehicle that has an ABS from a longitudinal force even if the longitudinal force, in stead of a lateral force, in a steady state can be calculated with the use of the above-mentioned tire dynamic model.
Further, the above tire dynamic model, which can provide a cornering characteristic in a steady state by supplying a constant slip angle, is not capable of simulating a transient response of the lateral force which changes with time by making the applied load fluctuate in a time-series manner while keeping the slip angle constant. A transient response resulting from fluctuations in applied load of the cornering power (CP) which is the lateral force at a slip angle of 1° is a particularly important tire characteristic in evaluating vehicle behavior.
For example, when the applied load fluctuates in a vehicle during cornering, the resultant change in CP changes the steering characteristic and responsiveness of a vehicle. These characteristics of a vehicle therefore cannot be evaluated without taking into account the applied load dependency of the CP of a tire.